The field of the invention is pneumatic control valves and the invention relates more particularly to valves which provide a timed vacuum at an output port in response to an external force.
A valve which has many of these characteristics are shown in U.S. Pat. No. 4,373,838. A diaphragm in the middle of the first chamber moves when the vacuum on one side of the diaphragm is released by movement of a sensor diaphragm as the result of a small increase in pressure on one side of the sensor diaphragm. This increase in pressure on one side of the sensor diaphragm causes a slotted shaft to move laterally permitting the vacuum to be drawn on an output port. A needle valve draws a vacuum on one side of the first chamber returning the diaphragm to its original position and moving the slotted stem to its original closed configuration. This returns the output port to atmospheric pressure.